Evening @Damon36!
Thank you for reaching out to us with your payment information questions, I am elated to help!
In the myAT&T app in your phone, Go to Billing and payments > Change Billing & Payments > Change billing & payment options > Manage Stored Payment Methods > Select New Credit / Credit Card.
I appreciate your time today, and you letting me assist you! Have a great day!
Cesar, AT&T Community Specialist